(1) Field of the Invention
The present invention pertains to a head suspension for supporting a read/write head adjacent a rotating data storage device, and in particular to a monocoque head suspension and its method of construction.
(2) Description of the Related Art
Most personal computer systems today employ direct access storage devices (DASD) or rigid disk drives for data storage. A conventional disk drive contains a spindle that is rotated by an electric motor at several thousand revolutions per minute (RPM) while the disk drive is turned on. A plurality of magnetically coated recording disks are mounted on the spindle for rotation therewith at axially spaced positions along the spindle. The number of the disks and the composition of their magnetic material coating determines the data storage capacity of the disk drive.
Positioned adjacent the peripheries of the rotating disk is a head actuator column. The head actuator column has a plurality of actuator arms thereon, and each actuator arm supports one or more head suspensions that extend in cantilever fashion from the actuator arm to distal ends of the head suspensions. Dynamic storage devices, for example optical or magnetic read/write heads are supported on sliders at the distal ends of each of the head suspensions. The plurality of actuator arms and their associated head suspension support the read/write heads adjacent the top and bottom surfaces of each of the plurality of disks supported by the spindle.
There are basically two types of head actuators, rotary and linear actuators. The rotary actuator moves its head suspensions and their supported read/write heads across the surfaces of the rotating disks in an arc, where the linear actuator moves the head suspensions and their associated read/write heads across the surfaces of the rotating disks linearly. In both types of actuators, the read/write heads supported on the sliders at the distal ends of each of the head suspensions slide in unison on a cushion of flowing air (or flowing liquid in some systems) across the surfaces of the drivers rotating disks. The read/write heads store data received from the disk drive's controller on a selected track of a disk by aligning magnetic particles on the disk surface. The read/write heads retrieve data from a particular track of the disk by detecting the polarities of the magnetic particles that have already been aligned on the disk track.
Continuous improvements made to disk drives have resulted in an increase in the storage capacity of the disk and an increase in the speed of the drive in storing and retrieving data from the disk. As one example, the storage capacity of the disk has been increased by increasing the number of concentric tracks on the surfaces of the disk. Where the size of the disk is limited, increasing the storage capacity of a disk results in increasing the density of the tracks on the surface of the disk as well as increasing the density of information stored on each track. The increased data density on the disk permits increased data storage while maintaining and possibly reducing the size of the disk. However, the increased density of tracks on the disk requires that the read/write head be more closely controlled to prevent lateral off-track error. The increased density of data on each track requires that the read/write head fly closer to the disk. As the transducer head is moved closer to the surface of the rotating disk, it creates an increased danger of the transducer head contacting the surface of the disk, resulting in the friction created by the rotating disk contacting the head damaging the surface of the disk, and potentially effecting the data stored on the disk as well as potentially damaging the head itself.
It is a complicated problem to design a head suspension that can cantilever a transducer head from an actuator arm at a substantially constant position relative to a rotating disk surface with there being an extremely small clearance between the head and the rotating disk surface, with the clearance sometimes being only 0.1 micrometers (a human hair is 100 micrometers thick). The surface of a data storage disk is not perfectly flat. When rotating in the disk drive, the contours of the disk surface create disruptions in the air stream created above the rotating disk surface on which the transducer head glides or flies. When the head is flying over a single track of the disk to access information on that track, it must glide at its predetermined slider attitude relative to the disk's contours. With the disk rotating at a constant speed, the surface velocity of the disk and the velocity of the air stream created by its rotation increases as the transducer head supported by the head suspension is moved from the center of the disk toward the disk periphery. As the head suspension moves the transducer head between the center and periphery of the rotating disk, it must have sufficient rigidity to resist changes in the lift forces created by the changes in the velocity of the rotating disk air stream and by the differences in the surface contours of the disk to hold the head at a desired clearance over the surface of the rotating disk.
In addition to the varying lift forces exerted on the head suspension, the head suspension is also subjected to extreme stresses as the actuator arm moves the head suspension and its supported transducer head quickly from one concentric track of data to another. The head suspension must be sufficiently rigid to withstand the stresses caused by this rapid movement without deflecting appreciably. The head suspension must also resist vibration after its rapid movement which could cause the transducer head to miss or overshoot the intended track of data among the densely arranged concentric tracks. Also, while being moved, the head suspension must not twist due to torque exerted on the suspension. This can cause one edge of the slider to be positioned closer to the rotating disk surface than an opposite edge of the slider resulting in off-track error or the head missing the desired track of data to be accessed among the densely arranged tracks. Also, an increased number of tracks on the disk increases the potential for lateral off-track error if torsional twisting of the head suspension reaches its torsional resonance frequency In operation, forces exerted on a head suspension will cause it to twist in torsion about the center longitudinal axis of the load beam. The twisting causes the slider and read/write head supported by the load beam to swing or pivot through a curve laterally from side to side. Depending on how far the read/write head is spaced from the center axis of the load beam, the swinging motion of the slider is more pronounced and the gain of the torsional frequency is increased. This side to side motion can cause the read/write head attached to the slider to swing or pivot off the disk track it is desired to access, resulting in a lateral off-tracking error. To combat this problem requires increasing the torsional stiffness of the head suspension without appreciably increasing the mass of the head suspension, thereby increasing the head suspension's torsional resonance frequency.
Competing with the need for rigidity in the head suspension is the need to give the head suspension as low a mass as possible to reduce inertial momentum of the assembly created by its rapid positioning movements. A large mass can detrimentally affect the quick movement of the head suspension and can create overshoot of a head suspension.
It is also a practical consideration that the head suspension construction facilitate the placement of electrical conductors carrying the electrical signals to and from the transducer head. It is desirable that the head suspension permit these conductors to be attached to the assembly in a manner that reduces their movement and vibration as the head suspension is moved, which can cause fluctuating input and output impedances.
Applying a known principle that the stiffness of a head suspension increases in proportion to the third power of its thickness, common methods for increasing the rigidity of a head suspension have included bonding additional layers of stiffening materials to areas of the load beam of the head suspension where rigidity is required, or forming bent sidewalls or rails that extend longitudinally along the opposite lateral edges of the head suspension load beam where additional rigidity is needed. The drawback of each of these prior art methods is that they result in adding significantly to the overall mass of the head suspension.
The desire to increase the rigidity of head suspensions without appreciably increasing their mass has resulted in the box beam design of head suspensions such as that disclosed in copending application Ser. No. 08/723,510, filed Sep. 30, 1996, which is a continuation of application Ser. No. 08/216,494, filed Mar. 22, 1994, now abandoned, the former of which is assigned to the assignee of record and incorporated herein by reference. In this type of box beam design the load beam is layered with a stiffener where the stiffener has an interior area between opposite lateral flanges of the stiffener, the interior area having been stamped to displace the area relative to the opposite lateral flanges or to give the interior area a concave shape. When the stiffener is attached to the load beam along its opposite lateral flanges, a box section or interior chamber is interposed between the load beam and stiffener. In a variation of this construction, the load beam itself is stamped forming it with an interior area that is displaced from opposite lateral flanges of the load beam. Connecting a flexure to the load beam along its opposite lateral flanges forms the box section or interior chamber. However, these methods of manufacturing head suspensions are disadvantaged in that they require welding the load beam to a stiffener or flexure along the opposite lateral edges outside the stamped areas of the load beam or stiffener. This requires extra material to provide the flanges for the welds (and its associated mass) to be added to the head suspension and located at a large distance from the longitudinal axis of the load beam. This extra material and its mass adds very little additional torsional stiffness to the head suspension because it is flat, but contributes significantly to the longitudinal polar moment of inertia. These effects combine to lower the torsional resonance frequency of a head suspension manufactured in this manner.
It is therefore desirable to design a head suspension constructed in a manner that increases its torsional stiffness without appreciably increasing its mass, thereby increasing the torsional resonance frequency of the head suspension.